Add support for f-strings

CHANGES

@@ -11,3 +11,4 @@
 0.4.1   -- Added missing SourceGenerator.visit_arguments()
 0.5     -- Added support for Python 3.5 infix matrix
            multiplication
+0.6     -- Added support for Python 3.6 f-strings.

astor/code_gen.py

@@ -486,6 +486,48 @@ class SourceGenerator(ExplicitNodeVisitor):
         result.pop()
         result.append(self.pretty_string(node.s, embedded, result))
 
+    def visit_JoinedStr(self, node, nested=False):
+        if not nested:
+            self.write("f'")
+
+        def write_string(s):
+            if sys.version_info >= (3, 0):
+                escaped = s.encode('unicode-escape').decode()
+            else:
+                escaped = s.encode('string-escape')
+            self.write(escaped.replace("'", "\\'"))
+
+        for value in node.values:
+            if isinstance(value, ast.Str):
+                write_string(value.s)
+            elif isinstance(value, ast.FormattedValue):
+                self.write('{')
+                self.visit(value.value)
+
+                if value.conversion != -1:
+                    self.write('!%s' % chr(value.conversion))
+                if value.format_spec is not None:
+                    self.write(':')
+                    # Either a nested Str or JoinedStr can be here.
+                    if isinstance(value.format_spec, ast.Str):
+                        write_string(value.format_spec.s)
+                    elif isinstance(value.format_spec, ast.JoinedStr):
+                        self.visit_JoinedStr(value.format_spec, nested=True)
+                    else:
+                        kind = type(value).__name__
+                        assert False, 'Invalid node %s inside JoinedStr' % kind
+
+                self.write('}')
+            else:
+                kind = type(value).__name__
+                assert False, 'Invalid node %s inside JoinedStr' % kind
+
+        if not nested:
+            self.write("'")
+
+    def visit_FormattedValue(self, node):
+        self.visit_JoinedStr(ast.JoinedStr(values=[node]))
+
     def visit_Bytes(self, node):
         self.write(repr(node.s))
 

tests/test_code_gen.py

@@ -353,5 +353,15 @@ class CodegenTestCase(unittest.TestCase):
         """
         self.assertAstSourceEqual(source)
 
+    def test_fstrings(self):
+        source = """
+        f'{x}'
+        f'{x.y}'
+        f'{int(x)}'
+        f'a{b:c}d'
+        f'a{b!s:c{d}e}f'
+        """
+        self.assertAstSourceEqualIfAtLeastVersion(source, (3, 6))
+
 if __name__ == '__main__':
     unittest.main()